1. Field of the Invention
This invention relates to liners for primary vessels and more particularly to an extensible and compressible liner for a primary vessel which does not maintain structural support for that primary vessel.
2. Description of the Related Art
Liners are used for fluid, gas, vacuum and granular solids containment. Some types of liners are only used for containment and do not provide structural support of the pressure applied to the liner by the contents, ullage gas or vacuum. (It is understood, however, that these liners do provide support between small gaps in the surface of the primary vessel which are bridged by the liners.) This type of liner is the subject of the present invention.
Pressure is transmitted through the liner and is supported by other load paths. As such, this type of liner must flex, expand, and contract to follow the relative displacements of the supporting primary vessel without significantly altering the pressure distribution to the primary vessel and yet still fulfill its functional requirements. Such external primary vessels may include (by way of illustration and not limitation), for example the hull of the ship, the shell of an aircraft or a tank. Such liners may also be used with the primary vessel that provides internal support for the liner. An example of such an internal vessel (where the liner is external) is a vacuum bag supported by its contents or internal structure.
Requirements of both these external and internal liners usually include elastic behavior of the liner up to maximum strains, maximum operating pressure, cycle life and thermal environments. To accomplish their objectives, the liners are usually textured. Texturing, as defined herein, is a design to gather, stretch, compress, shear or a combination of the above, moving the planar sheet, which forms the liner, out of plane in the form of multiple waves, folds, or dimples. The resulting excess material allows the liner to fulfill its desired functions. Texturing of this type also provides for relatively easy manufacturing of simple and compound shaped liners by forming on assembly, forming during or after texturing, or a combination thereof.
Containment of cryogenic fluids in a primary vessel at normal or very hot temperatures is particularly problematic. Similarly, containment of a vacuum bag around insulation (in this instance serving as the primary vessel), presents challenging design obstacles. Both applications require large strains (0.010 to 0.020 inches per inch), many times the yield of most liner type of materials, to accommodate the thermal and applied load deformation of the primary vessel.
For applications involving hot or cryogenic temperatures, and for the leak tightness necessary for some gases or liquids, metal liners are required. Metal liners must also be thin to meet desired flexibility and weight requirements. Stretching thin foil is a manufacturing problem and leak tightness is also impaired. Therefore, the design in which most of the texturing of the sheet is produced by a minimum amount of gathering is desired, if not mandatory.
Another essential attribute of an extensible and compressible liner is that it must accommodate the three-dimensional and biaxial nature of the deformed structure. Thermal displacements are nearly equal in all directions. An idealized metal cylinder pressure vessel has a 5-to-1 expansion ratio between the circumferential and longitudinal directions. Therefore, the natural longitudinal versus transverse biaxial displacement of the texture design should be either both extensible (+/+) or both compressible (-/-). Many textures even produce -/+ and displacements similar to the Poisson's Ratio effects in monolithic metals. These types of textures also produce very rigid stiffness in non-longitudinal/transverse, 45.degree. directions. This type of action is unsuitable for the requirements previously stated.
Liners are very rarely made from one monolithic sheet, thereby necessitating the need for individual textured sheets to be attached to each other or to close-out edge members of the primary vessel. Where leak tightness is required, proper matching of the textures of adjacent sheets at the joints is essential. Complexities of the texture make this matching difficult. The requirement for this matching, for complete folds and for adapting to corners of the primary vessel, present a very formidable set of design requirements, heretofore believed to be insolvable for practical applications. As will be disclosed below, the liner of the present invention meets all of these requirements.
U.S. Pat. No. 3,184,094, entitled "Extensible Metal Sheets", issued to M. J. French et al., discloses an extensible unitary, continuous, fluid impermeable sheet including an enclosed area bounded entirely by non-intersecting but meeting corrugations in the sheet, which corrugations extend linearly beyond the enclosed area, and which corrugations are capable of flexing in response to thermal expansion of the sheet. However, the folds are relatively widely spaced, creating a complicated folding at the intersections of the multi-directional folding. Since the folds are far apart, substantial motion at each fold is required because of the non-textured material between the folds are rigid. Furthermore, the bends for the folds approach a full (180.degree.) fold which would be difficult to be utilized on thin metal liners, especially at the multi-directional folds at intersections. Additionally, the complexity of the folding disclosed in the '094 patent would limit applications to large scale patterns for producibility.
U.S. Pat. No. 3,547,302, entitled "Container for Liquified Gases", issued to R. G. Jackson et al., discloses a container for cryogenic liquids having load-bearing insulating walls backing up thin, flexible membrane walls which constitute the primary container. The membrane walls are attached at the corners to rigid angle-section anchoring members which are supported by the insulating walls, and which are sufficiently strong to transmit to the insulating walls, without appreciable deformation, all loads transmitted to them by the membrane walls.
U.S. Pat. No. 3,956,543, entitled "Shear Flexibility for Structures", issued to M. L. Stangeland, discloses a flexible sheet member having cross convolutions oriented 45.degree. to the shear vector with spherical reliefs at the convolution junctions. The Stangeland invention requires extensive stretching.
U.S. Pat. No. 1,808,590, entitled "Method of Manufacturing Paper, Pasteboard, Felt and the Like", issued to A. W. Andernach, discloses a process producing biaxial texturing which pertains mainly to processing fibrous products.
U.S. Pat. No. 1,968,088, entitled "Protective Lining for Vessels", issued to L. A. Mekler, discloses a corrugated liner for vessels. The Mekler device has a single corrugation and as such handles flexure in only one direction.
U.S. Pat. No. 3,088,621, entitled "Insulated Tank for the Storage and Transportation of a Cold Boiling Liquefied Gas", issued to E. H. Brown, addresses the biaxial flexure requirements of a cryogenic liner. However, the corrugation described in that patent requires forming and stretching.
U.S. Pat. No. 3,434,617, entitled "Liquid Storage Tank", issued to C. H. Sieders et al., addresses multi-directional expansion requirements. However, use of the widely spaced corrugations disclosed in the Sieders patent would require stretching to form the liner.
U.S. Pat. No. 4,025,599, entitled "Cuspated Sheet Forming", issued to D. G. Keith, discloses a process for forming thermoplastic sheets. The resulting geometry appears as an origami pattern obtained by thermoplastic deformation.
U.S. Pat. No. 4,012,932, entitled "Machine for Manufacturing Herringbone-Pleated Structures", issued to L. V. Gewiss, discloses a machine that includes consecutive feeding forming and bunching components by which a continuous band of flat sheet material, which may be prepleated longitudinally, is fed between a pair of endless forming assemblies which cooperate to form continuously a roughed-out shape of the final herringbone-pleated structure and which also advance to a bunching means positioned downstream from the forming assemblies.
U.S. Pat. No. 1,847,216, entitled "Packing", issued to C. R. Hubbard, discloses use of an origami type of folding in a "full fold on itself" condition. This produces a very dense and strong but flexible packing for heavy parts.